1. Field of the Invention
This invention relates to an improvement in the spun-bonded process for making nonwoven fabrics whereby uniform fabrics composed of crimped filaments are obtained. Fabrics made in accordance with the present invention have apparel-like qualities (i.e. soft hand, flexibility, washability, etc.).
2. Description of the Prior Art
It is well known in the art that nonwoven fabrics can be produced by a continuous process from a melt (hereinafter referred to as "Spun Point-Bonded Process" or simply as "SPB Process") comprising the steps of melt spinning continuous filaments from a fiber-forming polymer melt such as nylon or polyester, pneumatically attenuating the filaments, depositing the filaments onto a moving surface such as a moving foraminous belt, usually in a random pattern, to form a uniform web of unbonded filaments, advancing the web, point-bonding the filaments to provide a nonwoven fabric and, finally, collecting the resulting fabric. The term "point-bonding" as used herein means the process of bonding the filaments of the web at a substantial number of spaced points (points where filaments cross-over) so that a discrete pattern of spaced filament bonds is formed. The bonding may be effected by either chemical or mechanical means. Attenuation of the filaments and deposition thereof onto the moving surface are conventionally accomplished by passing the freshly extruded filaments through a pneumatically operated aspirator. The aspirator serves not only to withdraw the filaments from the spinneret at a rate sufficient to impart a jet stretch thereto but also to advance the filaments to the moving belt. In passing through the aspirator the filaments assume a bundle configuration. The highest quality fabrics are obtained when the filaments are separated from one another at the time they are deposited onto the moving surface. Accordingly, if desired or necessary, the filaments after leaving the aspirator and before reaching the belt may be spread apart (or separated) by conventional means, such as by applying an electrical charge thereto in the manner described in U.S. Pat. No. 3,967,118. Typically, the velocity of the filaments leaving the aspirator are in the range of from 3000 to 5000 yds/min (2743.2-4572 m/min.) and the equipment is arranged such that the period of time lapsing from the time the filaments leave the spinneret until they are deposited on the belt is considerably less than 0.5 second and is usually in the range of from 0.02 to 0.05 second.
While it would be expected that nonwoven fabrics composed of crimped filaments would have a softer hand and superior flexibility, drape, washability and generally better apparel-like qualities than corresponding fabrics composed of uncrimped filaments, a satisfactory technique for crimping filaments during the SPB Process has not heretofore been developed. Unless the crimp is developed in the filaments after they leave the aspirator and before they are deposited on the moving surface, the quality and uniformity of the resulting fabric are greatly reduced. If the crimp is developed while the filaments are in a bundle configuration (i.e. before they leave the aspirator), filament entanglement occurs causing rope-like structures to be formed, the filaments of which, cannot be separated by conventional separation means before the filaments are deposited on the moving surface. The presence of such structures greatly reduce the quality of uniformity of the resulting fabric. On the other hand, if the crimp is developed after the filaments are deposited on the moving surface, the crimping motion causes undesirable drawing-up, i.e., distortion or disruption, of the web configuration which in turn greatly reduces the quality and uniformity of the resulting fabric.